Azeotropic distillation for recov



l1g- 11, 1953 H. v. HEss ETAL 2,648,624

AZEOTROPIC DISTILLATION FOR RECOVERY OF' AROMATIC FRAc'sIoNs CONTAINING NAPHTHALENE Filed Feb. 1o, 1951 HOW/IPB V H555 @01965 ,5. AFA/OLD .BY-L03@ /fa A H 'A'r'ToNz'y Patented Aug. 11, 1953 UNITED STATES PATENT OFFICE AZEOTROPIC DISTILLATION FOR RECOV- ERY OF AROMATIC FRACTIONS CON- TAINING NAPHTHALENE l Application February 10, 1951, Serial No. 210,408

1 claim. 1

This invention relates to certain improvements in the azeotropic distillation of hydrocarbon oils to recover aromatic fractions rich in naphthalene.

Certain polar solvents including furfural, aniline and phenol, form minimum boiling azeotropes with parainic hydrocarbons boiling in the range of naphthalene and methyl naphthalenes. These solvents will also form azeotropes with other non-aromatic hydrocarbons boiling in the same temperature range as the naphthalenes.

In accordance With the invention hydrocarbon oil having a boiling range within about 300 to 500 F. is distilled with one of these azeotrope formers to distill overhead azeotropes of parafnic hydrocarbons and azeotropes of other non-aromatic hydrocarbons. These azeotrope formers do not form azeotropes with naphthalene or methyl naphthalenes or other aromatics in this boiling range, and these materials remain in the distillation residue.

The process is applied to charging stocks, such as oils obtained from catalytic or thermal cracking or reforming processes or to Virgin gas oil stocks, containing naphthalenes so as to obtain as distillation residue an aromatic fraction rich in naphthalenes.

An important feature of the invention is concerned with the recovery and re-use of the azeotrope former. This recovery is accomplished by subjecting distillate products containing the azeotropa-former to a ternary azeotropic distillation with water. By such distillation the hydrocarbon is separated from the azeotrope-former so that the hydrocarbon may be eliminated from the system and the azeotrope-former recycled.

This ternary azeotropic distillation is advantageous in preventing the build-up of W boiling hydrocarbons in a system in which the recovered azeotrope former is recycled to the distilling zone wherein the aromatics are concentrated. We nd that a ternary azeotropic distillation with water in the latter Zone is a disadvantage because under the temperature conditions required the presence of the Water results in a steam stilling effect which impairs the desired separation of the aromatics. Thus a ternary azeotropic distillation of a, cut from a catalytic cracking operation with furfural and water yielded a 'l5-92% sulfonatable residue product containing about 23 weight per cent naphthalene, While a binary azeotrope distillation of the same oil with furfural produced about 99% sulfonatable residue having a 41% naphthalene content. In accordance with the invention, therefore, the separation of the aromatics from the other hydrocarbons is effected with a binary azeotropic distillation with furfural, aniline, or phenol and the use of water in a ternary azeotropic distillation is restricted to the step of recovering the azeotrope former.

In an example of the invention a fraction from a catalytic cracking process having a boiling range from 360 to 450 F. and containing 10% (by Wt.) naphthalene and 2% (by Wt.) methyl naphthalene was subjected to azeotropic distillation with furfural with an overhead temperature of 320 F. The overhead vapors were condensed and a furfural-rich distillate was obtained containing 5.1% (by wt.) oil and 94.9% (by wt.) furfural. The oil contained 30% sulfonatable material and 0.20% naphthalenes. The aromatic concentrate Withdrawn from the still as residue contained 98.9% (by wt.) oil and 1.1% (by wt.) furfural. The oil contained sulfonatable material 4and contained 41% (by wt.) naphthalene and 5% (by Wt.) methyl naphthalenes. The naphthalene recovery, based on a naphthalene balance, was 99%.

The amount of azeotrope former employed to obtain a good concentration of the aromatics by azeotropic distillation varies with the particular composition of the oil from which the aromatics are to be recovered, but in general dosages in the ratio of about 3-10:1 will be found to give satisfactory results.

The accompanying drawing is a flow diagram illustrating a preferred embodiment of the invention.

In practicing the invention -a hydrocarbon oil fraction preferably having a boiling range Within the range of about 30D-500 F. and containing naphthalenes is subjected to azeotropic distillation with either furfural, aniline, or phenol as the azeotrope former. In describing the process by reference to the iiow diagram the process will be specifically described with the use of furfural as the azeotrope former. The hydrocarbon fraction containing the aromatics and other hydrocarbons is introduced through a charging line I0 to a fractionating column II. Furfural is admitted through a line I2. The lower section of the tower II is subjected to heating and the upper portion is `provided with cooling or refluxing. means to secure fractionation of the rising vapors. Azeotropes are formed between the paraiins and other non-aromatics and the furfural Which are removed as vapor to a condenser I3, and the condensate is collected in a receiver I4. The residue which consists of the aromatic concentrate is withdrawn through a line I5.

The distillate in receiver Ill collects in two layers, a hydrocarbon rich phase and a furfural 3 rich phase. The furfural rich phase is withdrawn through a line I6 and recycled through line I2 to the separating tower Il.

The hydrocarbon rich phase is directed through a line I7 to a recovery still I8. Water is introduced through line i9 and a ternary azeotropic distillation is carried on in the recovery still I8. The furfural contained in the hydrocarbon rich phase which is introduced to the tower I8 forms ternary azeotropes with the water and hydrocarbons which pass overhead as vapors to a condenser 29 and the distillate is collected in the receiving drum 2l. The bottoms withdrawn from tower i8 through line `-22 consist of hydrocarbo-n oil substantially free from fu'rfural. The distillate collecting in the receiver 2l settles in three layers, an oil rich phase, a water rich phase and a furfural rich phase. The oil and water phases are recycled through line 23 to th re'- covery still I8.

The furfural rich phase lis withdrawn from receiver 2l and directed through a line 26% to a stripping still 25 v(for the removal of water. In the fractionating tower 25 a water-furiural azeotrope is distilled overhead and water-'free furfural is withdrawn as a residue through a line 2G and is directed thence through line i2 to the fractionati'ng column l I. The vapors from tower 25 pass to a condenser 27 and the distillate is collected in Ya 'receiver 2B wherein it -is settled as a fu'rfural rich phase and a water phase. The furfuial rich phase is withdrawn through line 29 and recycled to the stripping still 25. The water phase is withdrawn through line 3B and is directed through line i9 to fractionater i8 or through a line l3| to a stripping tower In the tower '32 fthe small amount of furfural contained in the water is distilled overhead, condensed in a condenser 33 and collected in receiver gli from which it is recycled through line 35 to the settler 28. The water which is free from ur-'fural is withdrawn through a line 3e. Norina-lly a portion of the water withdrawn through line 3a is regularly directed through line i9 to the tower i8 and the other portion is directed to the stripper 32 for the purpose of water rejection.

Make-up water may be introduced to the systex'n as needed through line 31 and make-up fur'fural may be introduced as needed through a line 38.

By'inea'ns of ythe recovery system disclosed herein, Athe urfural employed in effecting the separation of the aromatic constituents from the non-aromatic components of the charge oil is substantially completely recovered and is recycled -in the process. The recycled furfural is moreover freed of hydrocarbons and there is no build=up 'of low boiling hydrocarbons in the systern.

As'indi-cative of the type Iof separa-tion accomplished by fthe ternary azeotropic distillation in the tower i8, van example may be given in which the top temperature of the tower was held at about 2110n F. lwith `collection of three phases in receiver 2l of the following composition:

Vol. Percent Percent Percent Phase Percent Oil Water Furfural Oil rich.Y 33 94 1 5 Water rich 46 Trace 94 6 Fufural rich 21 9 6 85 The tower I8 should ordinarily be operated at a top temperature of some 50 or more below the true initial boiling point of the feed stock to the process.

Although a preferred `embodiment of the in' vention has been described herein, it will be understood that various changes and modiical tions may be made therein, while securing to a greater or less extent some or all of the benets Yof the invention, without departing from the spirit and scope thereof.

We claim:

The method of concentrating aromatic hydro-4 carbone including 'naphthalene from hydrocarbon stocks boiling within a range of 30D-500 F. and containing non-aromatic hydrocarbons and aromatic hydrocarbons including naphthalene that comprises subjecting such hydrocarbon stock in the absence of steam to an azeotropic distillation with furfural in a binary azeotropic distillationzlone, maintaining a temperature therein to distill overhead binary .azeotropes :of none aromatic hydrocarbons and .furfuraJL withdrawing as residue the resultant .aromatic concentrate containing naphthalene, .collecting the riverhead distillate as a iururali-rich phase and -a hydrocarbon-rich phase, returning Vthe furfuralrich phase to the binary vazeotropic distillation zone, subjecting the hydrocarbon-rich *phase to azeotropic distillation 'with 'Water in a ternary azeotropic .distillation cone, maintaining a temperature the-rein to distill overhead ternary aseo tropes of hydrocarbons, furfuralland water, 'with drawing -oil as residue substantia'liy free from furiural, collecting the overhead `distillate Ia hydrocarbon-rich phase, a water.rich phase .and a ur`fural-rich phase, returning .thelhydrocarbcnrich and water-rich phases to the ternary ateotropic distillation cone, stripping :any contained water from the iurfuralrich phase and recycling the stripped v-fu'rfural to the 'binary azeotropic distillation zone.

V. HESS. GEORGE B.. ARNOLD. `LOUS ,KOVACH- References Cited in the le vof this patent 

